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+/*********************                                                        */
+/*! \file BitVectors.java
+ ** \verbatim
+ ** Original author: mdeters
+ ** Major contributors: none
+ ** Minor contributors (to current version): none
+ ** This file is part of the CVC4 prototype.
+ ** Copyright (c) 2009-2012  New York University and The University of Iowa
+ ** See the file COPYING in the top-level source directory for licensing
+ ** information.\endverbatim
+ **
+ ** \brief A simple demonstration of the solving capabilities of the CVC4
+ ** bit-vector solver.
+ **
+ **/
+
+import edu.nyu.acsys.CVC4.*;
+
+public class BitVectors {
+  public static void main(String[] args) {
+    System.loadLibrary("cvc4jni");
+
+    ExprManager em = new ExprManager();
+    SmtEngine smt = new SmtEngine(em);
+
+    smt.setOption("incremental", new SExpr(true)); // Enable incremental solving
+
+    // The following example has been adapted from the book A Hacker's Delight by
+    // Henry S. Warren.
+    //
+    // Given a variable x that can only have two values, a or b. We want to
+    // assign to x a value other than the current one. The straightforward code
+    // to do that is:
+    //
+    //(0) if (x == a ) x = b;
+    //    else x = a;
+    //
+    // Two more efficient yet equivalent methods are:
+    //
+    //(1) x = a ⊕ b ⊕ x;
+    //
+    //(2) x = a + b - x;
+    //
+    // We will use CVC4 to prove that the three pieces of code above are all
+    // equivalent by encoding the problem in the bit-vector theory.
+
+    // Creating a bit-vector type of width 32
+    Type bitvector32 = em.mkBitVectorType(32);
+
+    // Variables
+    Expr x = em.mkVar("x", bitvector32);
+    Expr a = em.mkVar("a", bitvector32);
+    Expr b = em.mkVar("b", bitvector32);
+
+    // First encode the assumption that x must be equal to a or b
+    Expr x_eq_a = em.mkExpr(Kind.EQUAL, x, a);
+    Expr x_eq_b = em.mkExpr(Kind.EQUAL, x, b);
+    Expr assumption = em.mkExpr(Kind.OR, x_eq_a, x_eq_b);
+
+    // Assert the assumption
+    smt.assertFormula(assumption);
+
+    // Introduce a new variable for the new value of x after assignment.
+    Expr new_x = em.mkVar("new_x", bitvector32); // x after executing code (0)
+    Expr new_x_ = em.mkVar("new_x_", bitvector32); // x after executing code (1) or (2)
+
+    // Encoding code (0)
+    // new_x = x == a ? b : a;
+    Expr ite = em.mkExpr(Kind.ITE, x_eq_a, b, a);
+    Expr assignment0 = em.mkExpr(Kind.EQUAL, new_x, ite);
+
+    // Assert the encoding of code (0)
+    System.out.println("Asserting " + assignment0 + " to CVC4 ");
+    smt.assertFormula(assignment0);
+    System.out.println("Pushing a new context.");
+    smt.push();
+
+    // Encoding code (1)
+    // new_x_ = a xor b xor x
+    Expr a_xor_b_xor_x = em.mkExpr(Kind.BITVECTOR_XOR, a, b, x);
+    Expr assignment1 = em.mkExpr(Kind.EQUAL, new_x_, a_xor_b_xor_x);
+
+    // Assert encoding to CVC4 in current context;
+    System.out.println("Asserting " + assignment1 + " to CVC4 ");
+    smt.assertFormula(assignment1);
+    Expr new_x_eq_new_x_ = em.mkExpr(Kind.EQUAL, new_x, new_x_);
+
+    System.out.println(" Querying: " + new_x_eq_new_x_);
+    System.out.println(" Expect valid. ");
+    System.out.println(" CVC4: " + smt.query(new_x_eq_new_x_));
+    System.out.println(" Popping context. ");
+    smt.pop();
+
+    // Encoding code (2)
+    // new_x_ = a + b - x
+    Expr a_plus_b = em.mkExpr(Kind.BITVECTOR_PLUS, a, b);
+    Expr a_plus_b_minus_x = em.mkExpr(Kind.BITVECTOR_SUB, a_plus_b, x);
+    Expr assignment2 = em.mkExpr(Kind.EQUAL, new_x_, a_plus_b_minus_x);
+
+    // Assert encoding to CVC4 in current context;
+    System.out.println("Asserting " + assignment2 + " to CVC4 ");
+    smt.assertFormula(assignment1);
+
+    System.out.println(" Querying: " + new_x_eq_new_x_);
+    System.out.println(" Expect valid. ");
+    System.out.println(" CVC4: " + smt.query(new_x_eq_new_x_));
+  }
+}